1. Field of the Invention
The present invention relates to a zoom lens and an optical apparatus incorporating the zoom lens, and, more particularly, to a zoom lens and an optical apparatus appropriate for use in lens-shutter cameras, video cameras, and digital still cameras.
2. Description of the Related Art
As lens-shutter cameras, video cameras, and digital still cameras become compact in size, the need for a compact zoom lens having a high zoom ratio and a short overall length (from a lens surface of a first lens to the image plane) is mounting.
With advances in peripheral circuits such as the electronic circuit for zoom lens driving, cameras, in particular, lens-shutter, cameras have been substantially miniaturized. Accordingly, a high zoom ratio and compact design are required of the zoom lens as a photographing lens.
Three-unit zoom lenses, each composed of three lens units of positive, positive, and negative refractive power and having a high zoom ratio have been disclosed, for example, in Japanese Patent Laid-Open No. 4-37810 (corresponding to U.S. Pat. No. 5,166,828), Japanese Patent Laid-Open No. 4-76511 (corresponding to U.S. Pat. No. 5,216,547), Japanese Patent Laid-Open No. 8-262325 (corresponding to U.S. Pat. No. 5,721,643), and Japanese Patent Laid-Open No. 9-120028 (corresponding to U.S. Pat. No. 5,793,535).
Four-unit zoom lenses, each composed of four units of negative, positive, positive, and negative refractive power and having a high zoom ratio at a relatively wide view angle, have been disclosed, for example, in Japanese Patent Laid-Open No. 4-237009, Japanese Patent Laid-Open No. 9-15499 (corresponding U.S. Pat. No. 5,587,840), and Japanese Patent Laid-Open No. 10-31155.
Generally, the increasing of the refractive power of the zoom lens reduces the amount of travel of each lens unit to result in a given zoom ratio, and shortens the overall axial length of the lens system, while still achieving a high zoom ratio.
If the refractive power of each lens unit is increased, variations in aberrations increase during zooming. Particularly with a high zoom ratio, cameras cannot provide excellent optical performance over an entire zoom range.
The above-mentioned three-unit zoom lens, composed of the three lens units of positive, positive, and negative refractive power for use in a photographing system in the lens-shutter camera, performs a zooming operation by mainly changing the air spacing between a second lens unit of positive refractive power and the third lens unit of negative refractive power, and performs a further zooming operation by narrowing the air spacing between a first lens unit of positive refractive power and the second lens unit of positive refractive power toward the telephoto end. At the same time, the curvature of image is corrected during the zooming operation.
With a high zoom ratio, chromatic aberration becomes problematic during the zooming operation. To accomplish a high image quality, a good correction state must be maintained for the chromatic aberrations generated by the lens units. To keep good the correction state for the chromatic aberrations, the amount of chromatic aberrations must be reduced. A number of lens elements must be increased to correct chromatic aberrations.
To meet the compact design and high image quality requirements with an even higher zoom ratio, some optical arrangements need to be implemented in the above mentioned four-unit zoom lens composed of four lens units of negative, positive, positive and negative refractive power.
It is an object of the present invention to provide a zoom lens and an optical apparatus incorporating the zoom lens which is composed at least four lens units, and offers excellent optical performance over a full zoom range by properly setting the manner of movements of and refractive power of the lens units.
To achieve the above object, a zoom lens of the present invention includes from the object side a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of positive refractive power, and a fourth lens unit of negative refractive power. A zooming operation is performed by axially moving the lens units so that the spacing between the first lens unit and the second lens unit becomes wider at the telephoto end than at the wide-angle end, the spacing between the second lens unit and the third lens unit becomes wider at the telephoto end than at the wide-angle end, and the spacing between the third lens unit and the fourth lens unit becomes narrower at the telephoto end than at the wide-angle end. The following conditions hold:
1.0 less than F12w/Fw less than 2.5xe2x80x83xe2x80x83(1) 
0.6 less than F3/Fw less than 1.3xe2x80x83xe2x80x83(2) 
0.4 less than |F4/Fw| less than 0.7xe2x80x83xe2x80x83(3) 
xe2x80x830.01 less than |F2/F1| less than 0.16xe2x80x83xe2x80x83(4)
where Fw represents the focal length of the entire lens system at the wide-angle end, Fi represents the focal length of an i-th lens unit, and F12w represents the composite focal length of the first lens unit and the second lens unit at the wide-angle end.
Further objects, features, and advantages of the present invention will be apparent from the following description of the preferred embodiments with reference to the attached drawings.